xvi Remedial Measures and Insecticides. 



tion, which lessens danger of injury. Mr. Lounsbury writes, in his 

 Report of June 1897, ' Injury to the tips of new growth generally 

 results. This injury is in no wise serious, and is quickly outgrown. 

 The operators consider it a favourable indication, as when such 

 injury results it is quite certain that the gas has been present in 

 sufficient strength to destroy all of the insects.' 



With respect to fruit, I again quote from Mr. Lounsbury's 

 letter : ' I had lemons and oranges analysed after treatment, and 

 found that after a few hours not more than a trace of the gas 

 remained in the rind. There is much more natural cyanogen in a 

 single seed (so the analyst told me) than what remains in the fruit 

 from fumigation. We have no complaints of any effect on the 

 keeping qualities of the fruit.' 



To generate the gas ' the required quantities of cyanide and 

 water are first placed in the generating vessel, the cyanide being 

 broken into small pieces about the size of lump sugar. The 

 operator then adds the acid, pouring it slowly into the vessel to 

 avoid splashing, and immediately withdraws.' 



The above treatment is suitable for fruit and hardy plants. 

 Tender garden plants are usually imported in Wardian cases, and 

 may be treated separately. We have — in the ' Wardian case ' — an 

 air-tight chamber ready to hand, in which the plants can be 

 fumigated before their removal. After a large series of experi- 

 ments with various fumigating media, I find that hydrocyanic acid 

 gas remains by far the most efficient insecticide and the least 

 injurious to the plants. But with delicate succulent plants I find 

 it has to be applied rather differently. A more concentrated dose 

 of the gas applied for a shorter period is most satisfactory in its 

 results. In a Wardian case, containing about sixteen cubic feet, 

 I find a dose of \ ounce cyanide, \ ounce acid, and i ounce water, 

 with an exposure of half an hour, will kill every individual of a 

 colony of Orthezia (the most resistcnt of all Coccids) without in 

 the least affecting the plants. The treatment should be carried 

 out only after sunset. According to Mr. Lounsbury's tables, these 

 proportions of chemicals should be sufficient for a space of 140 

 cubic feet with a longer exposure. 



The other materials tested were (i) a preparation of concen- 

 trated nicotine, sold by the XL-all Company; (2) McDougall's 

 fumigation paper; (3) Jeyes' fluid ; (4) naphthaline; and (5) common 

 tobacco leaves. Nos. i, 3, and 4 were evaporated by means of a 

 small spirit lamp inside the case ; Nos. 2 and 5 were lighted and 



